Thermal cut-out



A. R. HAND THERMAL CUT-OUT July 9, 1935.

Original Filed Aug. 24, 1931 I' "IIMI IIIIIIIIIII II)IiIIIIIII/h IYWVQYHZOT":

Arthur R Hemcl, y MMMJMJZM His Attorney.

Patented July 9, 1935 PATENT OFFICE THERMAL CUT-OUT Arthur a. mammal Lake, N. Y., assignorto General Electric Company, a corporation of New York Application August 24, 1931, Serial No. 558,903 Renewed January 22, 1935 7 Claims.

My invention relates to fusible cutouts or fuses and more specifically to tension fuses of low current rating for high voltage circuits.

- Tension fuses have been used for high voltage 5 circuits with a spring directlyconnected to the fusible element to separate the severed ends upon the blowing of the fuse. While this method of connecting the fusible element directly to the tension device is satisfactory when the fusible l element is large, considerable difficulty is encountered when the rating of the fuse requires a fusible element which is small in that it does not have sufficient tensile strength to withstand the spring tension.

The object of my invention is to provide a tension fuse for high voltage circuits in which a fusible element connected to the spring may be made any size to withstand the spring tension regardless of the current rating of the fuse with 20 auxiliary means to cause the severing of the fusible element at the rated current of the fuse.

What I consider to be novel and my invention will be better understood by reference to the following specification and appended claims.

In the accompanying drawing, Fig. l is a cross sectional view of a fusible cut-out embodying my 7 invention, and Fig. 2 is an enlarged cross sectional view of the ends of the fuse at right angles to the view in Fig. 1.

In accordance with my invention, the main fusible element is made large enough to With* stand the requisite tension and an auxiliary pilot filament is connected in series with the main fusible element but relieved of all tension 5 so that it will be melted by the overload on the circuit and will cause a subsequent rupture of the main fusible element.

The cut-out comprises a shell Ill of insulating material which is substantially filled with an incombustible material or filler H which may be a mixture of calcium sulphate and calcium carbonate, or other suita le material. A fluid may be used as a substitute for the granular filler shown in the drawing. To retain the filler H 45 within the shell l0, metallic cups l2 and I3 are (Cl. 201F117) cup l3, and is connected .to a spring driven drum. l8 journalled in slots in cup l3. As best indicated in Fig. 2, the central opening in the end cup l2 through which the fusible element l6 passes is larger than necessary to permit the 5 passage of the fusible element and serves as an arcing edge, as will be explained later. An auxiliary fusible element or pilot filament I9 is connected to the fusible element l6 adjacent its point of anchorage and is connected to the end 10 cup l2 near the central opening.

Contact caps and 2| are provided for enclosing the ends of the shell and to make electrical connection with the circuit which the fuse is used to protect. These contact caps are se- 15 cured in position and electrically connected with the end cups l2 and 13 by means of screws threaded into apertures in the end cups. Circular openings or vents are provided in the contact caps to permit the escape of gases gener- 2 ated upon the blowing of the fuse.

In order to guide the fusible element through the enlarged central opening in end cup l2, and at the same time prevent the escape of the filler through the enlarged opening, a plate 22 of in- 25 sulating material having a small central opening somewhat larger than fusible element Hi to permit its easy passage is pressed within a central cavity of the cup. Crinoline discs 23 may also be placed between the filler and end cups in order to prevent the loss of the filler through the vents l4 and I5 provided in the end cups.

Spring driven drum I8 is mounted on a shaft 24 and adapted to rotate freely thereon. Shaft 2| is secured rigidly in slots in the projecting end of cup l3 and may be secured in position against rotation by soldering or welding it to the end cup. Drum I8 is driven by a spiral spring 25 which is connected at its inner end to shaft '24 and at its outer end to the outer periphery 40 of the drum H3.

The space between the end cup l2 and contact cap 20 where the pilot filament and fusible element are blown is generally termed the explosion chamber. In order to prevent an are within this chamber being drawn between the fusible element and the contact cap 20 a sleeve 26 of insulating material and a cooperating disc 21 also of insulating material are placed within the contact cap. Insulating disc 21 has openings cooperating with the openings in the contact cap to permit the escape of gases.

It may be desirable to waterproof the shell ill to prevent moisture or water impregnating the shell which would tend to make the shell 66 strikes the fusible element.

conducting and complete a path for current along the surface of the shell between the end caps.

The electrical circuit through the fuse extends from the contact cap 20 through the end cup l2, pilot filament I9, fusible element l6, spring wound drum l8, spring 25, shaft 24, end cup l3 to contact cap 2|. When the current flowing through the fuse is in excess of the rating of the fuse the pilot filament I9 is melted. This interrupts the metallic circuit through the fuse between the end cup l2 and the fusible element l6. As the pilot filament l9 melts, gases are generated and an are set up. This causes the drawing of an are between the end cup 12 and the fusible element I6. Since the shortest distance between the enclcup I2 and the fusible element I6 is at the point of passage of the fusible element through the central opening or arcing edge of the end c'up, the arc will be concentrated between this arcing edge and the adjacent portion of the fusible element and will cause a rapid melting of the fusible element due to the intense heat at the point the are When the fusible element is ruptured, spring driven drum l8 will be releasedand will rapidly coil the fusible element around it as it rotates and thus will draw out the are from the end cup I2 through the filler II. The filler II will serve to cool the rapidly elongating arc and quickly, quench it. The protected circuit will thus-be interrupted quickly without the generation of a large amount of heat and possible damage to ad jacent apparatus.

From the foregoing it may be seen that by the arrangement of a main fusible element of sumcient tensile strength to withstand the spring tension, and an auxiliary fusible element or pilot filament not subjected to any spring tension which may be made small enough to be blown by any desired overload and Will cause a subsequent blowing of the main fusible element, a fuse is provided that may be used to protect a high voltage circuit regardless of how small the current rating of the fused circuit may be and which is reliable and quick acting.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electric cutout comprising a shell of insulating material, a fusible element extending within said shell, a spring driven drum connected to one end of the fusible element, a pilot filament, and means for severing the fusible element upon the blowing of the pilot filament.

2. An electric cut-out comprising a shell of insulating material, a fusible element extending within said shell, a chamber containing a filler of incombustible material, a spring driven drum connected to one end of the fusible element and adapted to withdraw it through saidchamber upon the rupture of the opposite end, a pilot filament, and means for severing the fusible element upon the blowing of the pilot filament.

3. An electric cut-out comprising a shell of insulating material, an incombustible material substantially filling said shell, an explosion cham-.

ber in one end of the shell, a springmounted in the other end of the shell, a fusible element extending from said explosion chamber through the incombustible material and connected to the spring, a metallic cup located in the explosion chamber and having an enlarged central opening through which the fusible element passes, and a pilot filament connected between the fusible element and the metallic cup, whereby an arc is drawn between the metallic cup and the fusible element upon the blowing of the pilot filament tosever the fusible element.

4. An electric cut-out comprising a shell of insulating material, an incombustible material substantially filling said shell, an explosion chamber in one end of the shell, a spring driven drum mounted in the opposite end of the shell, a fusible element extending from the explosion chamber through the incombustible material and connected to the spring driven drum, a metallic cup located in the explosion chamber and having an enlarged central opening through which the fusible element passes, and a. pilot filament connected between the fusible element and the metallic cup, whereby an arc is drawn between the "central opening of the metallic cupand the fusiment passes, and a pilot filament connected between the fusible element and the metallic cup, whereby an arc is drawn between the arcing edge of the metallic cup and the fusible element upon the blowing of the pilot filament to sever the fusible element.

6. An electric cut-out comprising a shell, a fusible element extending within said shell, means placing the fusible element under tension, a pilot filament connected at one end tothe fusible element, and means to cause an arc to strike to the fusible element upon the blowing of the pilot filament.

'7. An electric cut-out comprising a shell, a fusible element extending within said shell, means placing the fusible element under tension, a pilot filament connected at one end to the fusible element and adapted to melt before the fusible element, and means to cause an arc to strike to the fusible element and sever the fusible element upon the blowing of the pilot filament.

ARTHUR R. HAND. 

